The Pumas were humiliated 73-13 by the Springboks in Soweto last weekend, a nine-try record Rugby Championship mauling in which, players admitted, they had been broken by their opponents.
Argentina cannot realistically aspire to a repeat of the 16-16 draw they managed a year ago in their debut season against the same opponents at the same Malvinas Argentinas stadium (1910 GMT).
But all week they have talked up their will to recover their trademark strengths in defence, set pieces and never-say-die attitude and Bosch said that wanting to expand their game might have worked against them.
"Maybe last year we also lost matches by big scores but I felt the team were there and confident in what they were doing. Last Saturday it was different," Bosch said.
"What we had been building for a long time was broken," he told reporters after a midweek practice.
"We weren't mentally prepared to handle what was happening to us. The challenge is to recover our identity in defence, which served us so well last year, and our game with the pack.
"Set pieces nowadays are essential, you can't play without them. You can't play a maul or scrum going backwards all the time, or a lineout that doesn't guarantee you quality balls to launch your game.
"Last year we had two good matches against (South Africa). We left the pitch strong and thinking we could do more," Bosch added.
"Maybe (last Saturday) we were aiming a lot at improving our attacking play and, unconsciously, we forgot about what makes this team strong, our identity which is defence and set pieces."
Argentina will recall that after their two good matches, despite losing, away to New Zealand and Australia last year, they tried to give more rein to their attack against the All Blacks in La Plata and conceded seven tries in a 54-15 defeat.
South Africa coach Heyneke Meyer is not taking anything for granted and is expecting the Pumas to be lifted by their home crowd.
"We experienced first-hand how passionate their supporters are and how they can lift their team," he said.
"Our focus is on continuous improvement and we would like to keep on converting try-scoring opportunities, building on our good on-field discipline and improving our play at the breakdowns."
Argentina's five changes for the match have been dictated more by injuries than the massive defeat because fullback Juan Martin Hernandez and lock Patricio Albacete, who came off in the opening half hour and have not recovered, would have kept their places.
The only tactical changes are the withdrawal of prop Matias Diaz to bring back Marcos Ayerza, who missed the Soweto match with cartilage trouble, and a preference on the left wing for Horacio Agulla over Juan Imhoff.
South Africa have stuck with a winning team, their only change being scrumhalf Jano Vermaak coming into the replacements for Fourie du Preez.
It is the second game for the teams in the competition. They both travel next to face Australia and New Zealand before hosting the two countries in late September and early October.
Argentina: 15-Lucas Gonzalez Amorosino, 14-Gonzalo Camacho, 13-Marcelo Bosch, 12-Felipe Contepomi (captain), 11-Horacio Agulla, 10-Nicolas Sanchez, 9-Martin Landajo; 8-Leonardo Senatore, 7-Juan Manuel Leguizamon, 6-Pablo Matera, 5-Mariano Galarza, 4-Julio Farias Cabello, 3-Juan Figallo, 2-Eusebio Guinazu, 1-Marcos Ayerza
Replacements: 16-Agustin Creevy, 17-Nahuel Lobo, 18-Matias Diaz, 19-Tomas Lavanini, 20-Benjamin Macome, 21-Tomas Cubelli, 22-Santiago Fernandez, 23-Juan Imhoff
South Africa: 15-Willie le Roux, 14-Bjorn Basson, 13-JJ Engelbrecht, 12-Jean de Villiers (captain), 11-Bryan Habana, 10-Morne Steyn, 9-Ruan Pienaar; 8-Duane Vermeulen, 7-Willem Alberts, 6-Francois Louw, 5-Juandre Kruger, 4-Eben Etzebeth, 3-Jannie du Plessis, 2-Adriaan Strauss, 1-Tendai Mtawarira
Replacements: 16-Bismarck du Plessis, 17-Gurthro Steenkamp, 18-Coenie Oosthuizen, 19-Flip van der Merwe, 20-Siya Kolisi, 21-Jano Vermaak, 22-Pat Lambie, 23-Jan Serfontein.
Referee: Steve Walsh (Australia)